Using tag calcs in reporting - range is same as maximum and minimum values

I am trying to create an uptime report using the tag calculation query. I am counting lifetime run hours on the machine and wanting the start hours, stop hours and the difference and put it in a table. I have it the way I want it other than if the value doesn’t change over the time period the range is the same value as the min and max instead of 0. Example- if I have 4015 machine hours at the beginning of the shift and we don’t run it so it still has 4015 at end of shift, the range is saying 4015 and should be 0. Has anyone else run into this or have a fix for it?